The objective is to determine the processes affecting cellular repair of DNA and their effects on radiation responses of cells, particularly to solar ultraviolet radiation. Attention is focussed on processes affected by radiation at wavelengths other than those doing the damage, which complicate predictions of solar UV damage on the basis of laboratory measurements. Specific aims involve characterization of enhanced DNA repairs induced by near UV light exposure, sequencing the gene for the enzyme responsible for photoenzymatic repair of pyrimidine dimers in DNA, and insertion of this gene into UV-sensitive mammalian cells on a plasmid which should secure its expression.